JP4936847B2 - Polyamide multilayer film - Google Patents

Description

  The present invention relates to a polyamide-based multilayer film used for packaging food or the like.

  Polyamide-based multilayer films containing nylon resins are excellent in gas barrier properties, toughness, pinhole resistance, etc., and are widely used in various fields. In particular, when used for packaging films such as food, high aroma retention, moisture proofing, gas barrier properties, toughness, wear resistance, etc. are required in order to prevent deterioration of the contents and deterioration of commercial value. A film with various improvements is known (see, for example, Patent Document 1).

  However, such films are often addressed by increasing the number of layers that are constructed to impart the desired properties. When the number of constituent layers increases, there is a problem that it is difficult to adjust the thickness of the film, which requires time and effort for production and increases production cost. In addition, the increase in the number of layers constituting the film complicates the equipment required for film production and increases the capital investment, and the maintenance and maintenance of the equipment is troublesome.

From such a background, a film having a small number of layers and excellent gas barrier properties, toughness, pinhole resistance and the like has been demanded.
JP-A-7-89025

  The main object of the present invention is to provide a polyamide-based multilayer film having three layers of polyamide layer / barrier layer / polyamide layer and excellent in stretchability, pinhole resistance and the like.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that a polyamide-based multilayer film comprising three layers of polyamide layer / barrier layer / polyamide layer is a blended resin comprising a combination of specific resins in the polyamide layer. It was found that a polyamide-based multilayer film excellent in stretchability and pinhole resistance can be obtained by using. The present invention has been completed as a result of further research based on this finding.

The present invention provides the following polyamide multilayer film and a packaging bag using the film.
Item 1. A polyamide-based multilayer film comprising three layers of polyamide layer / barrier layer / polyamide layer, the polyamide layer comprising 50 to 97% by weight of nylon 6, 3 to 30% by weight of nylon 6-66 copolymer and 0 A polyamide-based multilayer film composed of a mixture of up to 20% by weight of aromatic polyamide.
Item 2. Item 2. The polyamide-based multilayer film according to Item 1, wherein the aromatic polyamide is a crystalline aromatic polyamide or an amorphous aromatic polyamide.
Item 3. Item 3. The polyamide-based multilayer film according to Item 1 or 2, wherein the crystalline aromatic polyamide is polymetaxylene adipamide (MXD-nylon).
Item 4. Item 3. The polyamide multilayer film according to Item 1 or 2, wherein the amorphous aromatic polyamide is a copolymer of hexamethylenediamine-terephthalic acid-hexamethylenediamine-isophthalic acid.
Item 5. Item 5. The polyamide multilayer film according to any one of Items 1 to 4, wherein a copolymerization ratio of nylon 66 in the nylon 6-66 copolymer is 5 to 40 mol%.
Item 6. Item 6. The polyamide-based multilayer film according to any one of Items 1 to 5, which is a multilayer film obtained by biaxial stretching 2.5 to 4.5 times in the MD direction and 2.5 to 5 times in the TD direction.
Item 7. Item 7. The polyamide multilayer film according to any one of Items 1 to 6, wherein a total thickness of the polyamide multilayer film is 10 to 50 µm.
Item 8. Item 8. The polyamide multilayer film according to any one of Items 1 to 7, wherein a seal layer is laminated on one surface.
Item 9. Item 9. A packaging obtained by bonding the both ends of the polyamide-based multilayer film according to any one of items 1 to 8 so as to form a cylindrical shape, and further bonding one end of the opening of the cylindrical material. bag.
Item 10. Item 10. The packaging bag according to Item 9, which is for food packaging.

  According to the present invention, a polyamide-based multilayer film having excellent stretchability and pinhole resistance can be provided even with a very simple configuration of three layers (polyamide layer / barrier layer / polyamide layer). That is, the polyamide-based multilayer film of the present invention is excellent in wear resistance, puncture strength, impact strength, and flex resistance in addition to high stretchability. The film of the present invention having such excellent characteristics hardly causes pinholes due to wear or the like even when transported and transported as a packaging bag, and can be suitably used particularly as a food packaging bag.

  In addition, since the film of the present invention has a simple structure with a small number of layers, it is easy to adjust the thickness of the film and the production process is simple, which is necessary for production cost and equipment input. Costs can be kept low.

1. Polyamide-based multilayer film The polyamide-based multilayer film of the present invention is a multilayer film comprising three layers of polyamide layer / barrier layer / polyamide layer.
(1) Polyamide layer In the polyamide-based multilayer film of the present invention, the polyamide layer comprises (i) nylon 6 and nylon 6-66 copolymer, or (ii) nylon 6, nylon 6-66 copolymer and aromatic polyamide. It consists of a combination of

Nylon 6 is also called a polycapramide, and a commercially available one can be used, and is not particularly limited. According to JISK 6810, 96% H ₂ SO ₄ , 1.0 g / 100 ml, temperature 25 ° C. It is preferable to use those having a relative viscosity of 2 to 6, preferably 2 to 5 under the conditions of Examples of such nylon 6 include 1022FDX04 (manufactured by Ube Industries). The blending amount of nylon 6 in the polyamide layer is about 50 to 97% by weight, preferably about 65 to 97% by weight, and more preferably about 70 to 95% by weight.

The nylon 6-66 copolymer is also called a caprolactam / hexamethylene diammonium adipate copolymer, and a commercially available one can be used. Although not particularly limited, it is 96% according to JISK 6810. It is preferable to use one having a relative viscosity of 2 to 6, preferably 2 to 5 under the conditions of H ₂ SO ₄ , 1.0 g / 100 ml, and a temperature of 25 ° C. As such a nylon 6-66 copolymer, 5034B (made by Ube Industries, Ltd.) etc. can be used, for example. The copolymerization ratio of nylon 66 in the nylon 6-66 copolymer is about 5 to 40 mol%, preferably about 5 to 30 mol%, more preferably about 10 to 25 mol%. The blending amount of the nylon 6-66 copolymer in the polyamide layer is about 3 to 30% by weight, preferably about 3 to 25% by weight, more preferably about 5 to 20% by weight.

  As the aromatic polyamide, conventionally known ones can be used, and examples thereof include crystalline aromatic polyamides and amorphous aromatic polyamides.

  Examples of crystalline aromatic polyamides include aromatic diamines such as metaxylenediamine and paraxylenediamine, and dicarboxylic acids such as adipic acid, suberic acid, sebacic acid, cyclohexanedicarboxylic acid, terephthalic acid, and isophthalic acid, and derivatives thereof. The crystalline aromatic polyamide obtained by the polycondensation reaction is preferably polymetaxylene adipamide (MXD-nylon) or the like.

  As the amorphous aromatic polyamide, for example, an amorphous aromatic polyamide (amorphous) obtained by a polycondensation reaction between an aliphatic diamine such as hexamethylenediamine and a dicarboxylic acid such as terephthalic acid or isophthalic acid or a derivative thereof. Nylon) and the like, and preferably a copolymer of hexamethylenediamine-terephthalic acid-hexamethylenediamine-isophthalic acid.

  The compounding amount of the aromatic polyamide in the polyamide layer is about 0 to 20% by weight, preferably about 0 to 15% by weight, more preferably about 0 to 10% by weight.

  Preferred combinations of the polyamide layers in the multilayer film of the present invention include, for example, 50 to 97% by weight of nylon 6; 3 to 30% by weight of nylon 6-66 copolymer; 0 to 20% by weight of aromatic polyamide. is there.

(2) Barrier layer The barrier layer constituting the multilayer film of the present invention contains ethylene vinyl acetate copolymer saponified product (EVOH) as a main component.

  EVOH is not particularly limited, but the ethylene content is 55 mol% or less, preferably about 20 to 50 mol%, more preferably about 26 to 44 mol%, and the saponification degree of the vinyl acetate component is about 90 mol% or more. Preferably, about 95 mol% or more is suitably used.

  In addition, EVOH includes a small amount of an α-olefin such as propylene, isobutene, α-octene, α-dodecene, α-octadecene, etc .; an unsaturated carboxylic acid or a derivative thereof (in the range not adversely affecting the effects of the present invention). For example, it may contain a comonomer such as a salt, a partial alkyl ester, a complete alkyl ester, a nitrile, an amide, an anhydride); an unsaturated sulfonic acid or a salt thereof.

  The melt index (MI) of EVOH is preferably 0.5 to 50 g / 10 minutes (210 ° C., 2160 g load), and more preferably 1 to 35 g / 10 minutes (same as above). If the MI is 0.5 g / 10 min (same as above) or higher, the melt extrusion is not hindered. Conversely, if the MI is 50 g / 10 min (same as above) or less, the deterioration of the film forming property is suppressed. Can do.

  The barrier layer may be composed of EVOH. However, the barrier layer may be made of other aliphatic amide, modified ethylene vinyl acetate copolymer, methacrylic acid copolymer ionomer, etc. as long as the effect of the present invention is not adversely affected. It may contain components. When the barrier layer contains other components, the content of this component is usually 15 parts by weight or less, preferably about 1 to 7.5 parts by weight with respect to 100 parts by weight of EVOH or aromatic polyamide. preferable.

  The total thickness of the polyamide-based multilayer film of the present invention including the above three layers is about 10 to 50 μm, preferably about 10 to 30 μm, more preferably about 12 to 25 μm, and still more preferably about 12 to 20 μm. The total thickness of the two polyamide layers is about 3 to 49 μm, preferably about 6 to 29 μm, more preferably about 8 to 24 μm, and still more preferably about 10 to 15 μm. The thickness of the barrier layer is about 1 to 20 μm, preferably about 1 to 15 μm, more preferably about 1 to 10 μm, and still more preferably about 1 to 5 μm.

2. Manufacturing method of polyamide-based multilayer film The polyamide-based multilayer film of the present invention can be manufactured in accordance with a conventionally known method. For example, cooling water circulates from a T die so as to be in the order of polyamide layer / barrier layer / polyamide layer. Co-extruded on a chill roll to obtain a flat multilayer (three layers) film. The obtained film is stretched in the MD direction to about 2.5 to 4.5 times by a roll stretching machine at 50 to 80 ° C., for example, and further 2.5 to 5 times by a tenter stretching machine in an atmosphere at 80 to 140 ° C. It can be obtained by stretching in the TD direction to the extent and subsequently heat-treating in the 180-220 ° C. atmosphere with the same tenter. The multilayer film of the present invention is preferably stretched by biaxial stretching, and any of sequential biaxial stretching and simultaneous biaxial stretching may be employed. If necessary, the obtained multilayer film may be subjected to corona discharge treatment on both surfaces or one surface thereof.

3. Features of the polyamide-based multilayer film The polyamide-based multilayer film of the present invention produced as described above has wear resistance, puncture strength, impact strength, flex resistance, and heat shrink resistance in addition to high stretchability. Excellent pinhole resistance. Therefore, the multilayer film of the present invention is suitably used as a packaging film.

  Specifically, the polyamide-based multilayer film of the present invention has excellent characteristics as follows.

(I) Stretchability The polyamide-based multilayer film of the present invention is characterized in that the occurrence of stretch breakage is 2 times or less, and further 1 time or less in film formation for 24 hours.

(Ii) Abrasion resistance The polyamide-based multilayer film of the present invention is excellent in abrasion resistance due to repeated contact. This “abrasion resistance by repeated contact” is evaluated by the method described in Examples described later.
Specifically, the multilayer film is mounted on a conical aluminum jig, and the apex of the conical shape is brought into contact with the cardboard through the multilayer film. Next, a load of 10 to 120 g is placed on the jig and the humidity is 65% RH, and sliding is performed at a speed of 2700 mm / min within a moving distance of 45 mm. Count (see, for example, FIG. 1). The occurrence of pinholes is determined by dripping the penetrating solution where the top of the jig hits the film. Under such measurement conditions, in the multilayer film of the present invention, when the load is 63 g, the number of sliding times until the pinhole is opened is 350 times or more, and further 400 times or more. If it is 300 times or less, the wear resistance is low, and pinholes are likely to occur due to repeated wear during actual transportation.

(Iii) Puncture strength The polyamide-based multilayer film of the present invention is characterized by a puncture strength measurement according to JISZ-1707 of 7N or more, and further 8N or more.

(Iv) Impact Strength The polyamide-based multilayer film of the present invention has a feature that it is 0.7 J or more, and further 0.8 J or more in impact strength measurement by an impact tester.

(V) Flexural resistance The polyamide-based multilayer film of the present invention is 4/300 cm ² or less when the number of pinholes generated in a gelboflex test at 23 ° C. or 5 ° C. × 1,000 times is 23 ° C. Further, 2 pieces / 300 cm ² or less; at 5 ° C., 12 pieces / 300 cm ² or less, and further 6 pieces / 300 cm ² or less. Evaluation of pinholes by bending is as described in Test Example 1.

(Vi) Heat Shrinkage Rate The heat shrinkage rate after treating the polyamide multilayer film of the present invention with MD × TD = 100 mm × 100 mm with boiling water for 30 seconds is less than 2% in the MD direction, and further less than 1.6%. And less than 1.2% in the TD direction, and further less than 0.6%.

  When the polyamide-based multilayer film of the present invention is used as a packaging bag, for example, both ends are bonded so that the films are in close contact with each other so that the film has a cylindrical shape. A packaging bag can be obtained by similarly bonding one end of the opening of the object.

  At this time, it is preferable to previously laminate a sealing layer on one surface of the polyamide-based multilayer film. Further, although not particularly limited, it is desirable to bond the both ends of the film so as to be cylindrical, so that the TD direction of the film is a circumference. When the heat shrinkage rate in the TD direction is large, the lower end or upper end of the bag is excessively shrunk and looks bad, and it may be impossible to use as a bag. Since the multilayer film of the present invention has a small heat shrinkage rate, such a problem does not occur, and the product value, the customer's willingness to purchase, and the like can be enhanced.

  Here, the sealing layer may be a resin film having heat sealing properties, and examples thereof include conventionally known ones such as polyolefins such as LLDPE, LDPE, CPP, and EVA. As a method of laminating the polyamide-based multilayer film and the seal layer, a known method can be adopted. Also, a known method can be adopted as a heat sealing method.

  The contents to be packaged are not particularly limited, but the effects of the present invention are particularly remarkable when packaging heavy foods such as rice cakes, winners, seasonings, and frozen foods that are transported at low temperatures. Demonstrated.

  EXAMPLES Hereinafter, although an Example etc. are shown and this invention is demonstrated in detail, this invention is not limited to these.

  A polyamide-based multilayer film using a polyamide layer having the composition shown in Table 1 below and EVOH as a barrier layer was produced. The manufacturing method is as follows.

Example 1
Nylon 6 (95% by weight: 1022 FDX04 (manufactured by Ube Industries)) and nylon 6-66 copolymer (5% by weight; copolymerization ratio of nylon 66: 20 mol%: 5034B (manufactured by Ube Industries, Ltd.)) Thus, a resin composition constituting the first layer and the third layer was produced.

  Further, a saponified ethylene-vinyl acetate copolymer (ethylene content: 32 mol%, saponification degree: 99 mol%: DC3203FB (manufactured by Nippon Gosei Co., Ltd.)) was used as a resin constituting the second layer. The melt index of the saponified ethylene-vinyl acetate copolymer is 3.2 g / 10 min (210 ° C., 2160 g load).

  The resin composition constituting each layer is coextruded on a chill roll in which cooling water circulates from a T die so that the order is the first layer / second layer / third layer, and a flat three-layer film is formed. Obtained. This three-layer film was stretched in the MD direction by 3.0 times with a 65 ° C. roll stretching machine, then stretched in the TD direction by 4.0 times by a tenter stretching machine at 110 ° C., and further 210 by the same tenter. A film having a thickness of 15 μm was obtained by heat treatment in an atmosphere at 0 ° C. The thickness of each layer was 6.5 / 2 / 6.5 (μm).

(Examples 2-5 and Comparative Examples 1-6)
The film of Examples 2-5 and Comparative Examples 1-6 was manufactured by the same method as the said Example 1 according to the composition of following Table 1. The thickness of each film was also 15 μm (the thickness of each layer was 6.5 μm / 2 μm / 6.5 μm).

  In Table 1, hexamethylenediamine-terephthalic acid-hexamethylenediamine-isophthalic acid copolymer was used as amorphous nylon.

Test Example The polyamide-based multilayer film obtained as described above was evaluated according to the following method.

(1) Stretchability Stretchability was evaluated based on the number of stretch breaks that occurred in film formation for 24 hours. The evaluation criteria are as follows.
Number of break occurrences: 0 to 1 time… ○ 2 times… △ 3 times or more… ×

(2) Abrasion resistance It evaluated by the Gunze method. Specifically, it is as follows.
A film is attached to an aluminum jig having a conical shape using a tape or the like, and the apex of the conical jig is inserted into the cardboard through the film (430 g / m ² for KOKUYO Campus board eye beautiful pus). ). The vertex R was set to a sliding direction R = 0.1 to 1.0 mm and a direction R = 0.1 to 1.0 mm perpendicular to the sliding direction. Next, a load of 63 g was placed on the jig. Under the condition of humidity 65%, the jig was slid parallel to the cardboard at a speed of 2700 mm / min and within a moving distance of 45 mm, and the number of times of sliding until pinholes were formed was counted. The occurrence of pinholes was determined based on whether or not the penetrating solution was dropped onto the film where the top of the jig had hit and permeated on white paper.
FIG. 1 shows a schematic diagram of the measuring apparatus. FIG. 2 shows an example of a conical aluminum jig.
Abrasion resistance (number of sliding times) was measured in units of 50 times, and evaluated based on the number of times when the hole was opened (for example, 400 times when opening at 400 times and not opening at 350 times).
Number of sliding times: 400 times or more… ○ 350 times… △ 300 times or less… ×

(3) Puncture strength Measured according to JIS Z-1707.
8N or more… ○ 7N or more to less than 8N… △ less than 7N… ×

(4) Impact strength The impact strength of each film was measured with a film impact tester [manufactured by Toyo Seiki Seisakusho].
0.8J or more ... ○ 0.7J or more but less than 0.8J ... △ less than 0.7J ... ×

(5) Bending resistance The pinhole property by bending was evaluated using a gelbo flex tester manufactured by RIKEN. In this method, a film formed into a cylindrical shape with a folding diameter of 150 mm and a length of 300 mm is attached to a gelbo flex tester, and a straight horizontal movement of 62.5 cm is performed at a twist angle of 440 ° under normal temperature (23 ° C. or 5 ° C.) conditions. After repeating 1000 times below, the number of pinholes is examined using a penetrant. Note that the number of pinholes was measured at a location of 300 cm ^{2 at} the center of the sample that was twisted and bent. The number of pinholes was measured for three samples, and the average value was obtained.
23 ° C. (1,000 times): 0 to 2 pieces ○ 3 to 4 pieces Δ Five or more pieces ×
5 ° C. (1,000 times): 0 to 6 pieces ○ 7 to 12 pieces Δ Δ 13 pieces or more ×

(6) Thermal Shrinkage Rate A sample of MD × TD = 100 mm × 100 mm was treated with boiling water for 30 seconds, and the shrinkage rate after the treatment was measured.
MD: Less than 1.6% ... ○ 1.6% or more but less than 2.0% ... △ 2.0% or more ... ×
TD: Less than 0.6% ... ○ 0.6% or more but less than 1.2% ... △ 1.2% or more ... ×

The above evaluation results are shown in Table 2.

  In the above evaluation, Δ or more was regarded as acceptable. It was confirmed that the polyamide-based multilayer film of the present invention has excellent properties in all of stretchability, abrasion resistance, puncture strength, impact strength, flex resistance and heat shrinkage.

Schematic diagram of the measuring device used for wear resistance evaluation is shown. It is a figure which shows an example of a cone-shaped aluminum jig.

Claims (9)

A polyamide-based multilayer film comprising three layers of polyamide layer / barrier layer / polyamide layer, the polyamide layer comprising 50 to 97% by weight of nylon 6, 3 to 30% by weight of nylon 6-66 copolymer and 0 A polyamide-based multilayer film composed of a mixture of aromatic polyamide of ˜20% by weight , wherein the copolymerization ratio of nylon 66 in the nylon 6-66 copolymer is 5 to 40 mol% . The polyamide-based multilayer film according to claim 1, wherein the aromatic polyamide is a crystalline aromatic polyamide or an amorphous aromatic polyamide. The polyamide-based multilayer film according to claim 1 or 2, wherein the crystalline aromatic polyamide is polymetaxylene adipamide (MXD-nylon). The polyamide multilayer film according to claim 1 or 2, wherein the amorphous aromatic polyamide is a copolymer of hexamethylenediamine-terephthalic acid-hexamethylenediamine-isophthalic acid. The polyamide-based multilayer film according to any one of claims 1 to 4 , which is a multilayer film obtained by biaxial stretching 2.5 to 4.5 times in the MD direction and 2.5 to 5 times in the TD direction. The polyamide multilayer film according to any one of claims 1 to 5 , wherein a total thickness of the polyamide multilayer film is 10 to 50 µm. The polyamide-based multilayer film according to any one of claims 1 to 6 , wherein a seal layer is laminated on one surface. A packaging obtained by bonding both ends of the polyamide-based multilayer film according to any one of claims 1 to 7 so as to form a cylindrical shape, and further bonding one end of an opening of the cylindrical material. Bags. The packaging bag according to claim 8 , which is used for food packaging.

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